We have identified two insertional mutations in transgenic mice with developmental abnormalities. The inserted transgenes in these mutants provide a molecular tag for isolation of the affected genes. The first mutation we will analyze produces hyperactivity and circling behavior in heterozygotes, due to abnormalities of the vestibular apparatus of the inner ear. The transgenic insert in this line maps to proximal mouse Chr 18, in the region of the classical Twirler mutation. In addition to inner ear defects, the original Twirler mutant produces cleft lip and palate in homozygotes. We will determine whether our mutant is allelic with Twirler by complementation analysis. A genomic library has been constructed from this mutant, and will be used to isolate and characterize the affected gene. Exons will be identified by their conservation in other mammalian species and used as probes to isolate the cDNA. Antisera to synthetic peptides will be used to determine the craniofacial distribution of the gene product, and its subcellular localization. Linkage studies will determine the location of the homologous human gene and its relationship to human inherited palatal defects. Characterization of this gene in the mouse will provide molecular insight into developmental fusion processes. The second insertional mutation causes semidominant developmental abnormalities of the kidney including agenesis . The proposed investigations will provide molecular insight into two genes responsible for important developmental and clinical abnormalities. In addition, we will continue to screen for novel mutations in other transgenic lines and to characterize them by similar procedures. Insertional mutation in transgenic mice provides a powerful system for the identification and genetic mapping of new functional elements in the mammalian genome, and for molecular characterization of these new genes.